Some 200 municipal police officers in the eastern Mexican city of Cordoba gathered to protest the detention of two of their colleagues by marines.

The cops, who appeared in uniform with their service weapons, also complained of abuses suffered at the hands of the marines deployed to suppress rising gangland violence in the Gulf coast state of Veracruz.

The protesters demanded the release of Cordoba municipal officers Jose Manuel Hernandez and Filemon Alvarez Mendez.

Marines arrested the two men without a warrant, according to the police at the demonstration, which was led by the inspector of the municipal force, Hermilio Vargas Ziehl.

The protesting cops formed a motorcade of 22 patrol cars and 18 motorcycles and made an unsuccessful attempt to reach the marine barracks in the neighboring town of Fortin de Las Flores to rescue their comrades.

After being turned back, they decided to go to the regional office of the State Human Rights Commission to file a formal complaint about the "disappearance" of Hernandez and Alvarez.

The pressure finally led the marine unit to release the two police officers, who had been detained for lacking the proper permits to carry weapons.

Cordoba's mayor, Francisco Portilla Bonilla, said some of the city police lack gun permits because his predecessor's administration failed to appropriate money to obtain the necessary credentials from the Veracruz Public Safety Office.

"Our police carry a credential that we provide, which has the officer's name, his rank and the number to carry the weapon. But it is not the one that is authorized" by the state government, the mayor said.

Within days of taking office in December 2006, President Felipe Calderon gave the Mexican military the leading role in combating the nation's powerful drug cartels.

Tens of thousands of soldiers and marines have been deployed across Mexico to carry out tasks usually performed by civilian law enforcement.

Defenders of the policy point to pervasive corruption among state and local police forces, but some of the cops detained by the military on suspicion of colluding with the cartels say they were tortured to force them to confess to crimes they never committed.

There have also been reports about soldiers and marines sexually assaulting female police officers.